The present invention relates to a master cylinder for supplying operating fluid to a brake system of a vehicle, a master cylinder body, and a method of producing the master cylinder.
As a master cylinder for supplying operating fluid to a brake system of a vehicle, there is one of a structure in which a piston is directly fittingly inserted in a cylinder body of bottomed cylindrical shape, putting the sleeve for a cylinder in disuse. This type of a master cylinder comprises: a cylinder body of bottomed cylindrical shape, a supply passage provided in this cylinder body for supplying operating fluid therethrough from a reservoir; a pressure chamber defined inside the cylinder body by a piston which slides therein; a piston seal provided in a circumferential groove formed in the cylinder body, and having an inner circumference in sliding contact with the piston and an outer circumference which enables the operating fluid to be supplied from the supply passage into the pressure chamber; and a communication groove which opens into the circumferential groove and extends from this circumferential groove toward a bottom portion of the cylinder body to connect the pressure chamber side and the circumferential groove. This communication groove is formed with its center made eccentric relative to the center of the circumferential groove, and is provided to send the operating fluid, which is supplied through a portion between a bottom portion of the circumferential groove and the outer circumference of the piston seal, into the pressure chamber when the piston returns to its initial position after generating a fluid pressure in the pressure chamber. (See, for example, Japanese Patent Application Publication No. 2004-299568.)